Results of incubation-respiration experiments
-C from hydrochars are less stable than from biochars, being wood biochars those with the greatest C-sequestration potential.
-The average residence times of C from bio/hydro chars showed that they are less stable than initially assumed (not reach the centennial or even millennial timeframe reported by literature when concerning C stability in soils of char materials).
Preliminary results of hand-picked biochars sampled at field plots confirmed the findings from the Respicond experiment. Biochar particles were weathered much faster than assumed. NMR spectroscopy showed that in a period of time of less than 24 months the condensed structures of biochars are partially functionalized, the presence of carboxylic group support the quick aging of biochars.
Effect of biochar amendment on plant physiology and productivity under Mediterranean climate (field experiments)
Amendments with 15 t ha-1 slightly increased the water holding capacity of the soil but showed no lasting impact on the soil pH. It stimulated plant growth and led to a greater leaf area, larger plant stems and wider inflorescences of the sunflower plants than those cultivated on the un-amended soil. Moreover, as indicated by a reduced stomatal conductance, leaf transpiration decreased in biochar-amended plants compared with the non-amended ones. While reduced stomatal conductance of biochar-amended plants was not a consequence of a stress situation as indicated by the better plant growth, it correlated with higher stability of Photosystem-II, probably as a consequence of lower water use in a dry environment. At the end of the experiment, biochar amendment of soil caused no significant increase of the total biomass production excepting the biochar with the lowest capacity of water retention, which exhibited the highest vegetative growth and seed production, achieving better performance from an agronomic point of view under Mediterranean climate for this non-irrigated crop.
Results of this field experiment have been recently submitted to CATENA Journal.